Early efforts in style transfer first emerged from the patch synthesis school, appearing simultaneously in [1]} as a novel task and in [2]} as an extension of texture synthesis. In [2]} patches from different regions of style are guided to regions of the content with similar luminosity. In [1]} guidance is based on an 'unfiltered' version of the style which can be more easily matched to the photographic content image (e.g. a photograph of some apples on a table is the unfiltered style, and a watercolor painting of the same apples from the same viewpoint is the filtered style). Extending texture synthesis to heterogeneous style images using additional guidance is a powerful technique, and this approach is still influential today where it has led to state of the art algorithms in data-driven 3d rendering [5]}, [6]}.
